Human language, bat echolocation linked to the same gene

Scientists look at the bat version a gene associated with human language …

Those of you who followed news from biology a few years back are probably aware of reports of a "language gene." That gene, FOXP2, was found to be altered in families with a history of disabilities that included a striking lack of language skills. A further link to language skills came when the gene was examined in other great apes: chimps and gorillas had an identical version of the gene, while humans had two distinct changes in it. Further studies revealed that there have been very few changes in the gene throughout mammalian evolution. Since then, studies of the expression of and mutations in FOXP2 from a variety of species have suggest its involvement in hearing and facial muscle control as well, so the actual connection between the gene and language remains a bit of a mystery.

That mystery has deepened a bit with the publication of an Open Access paper in PLoS one that looks at FOXP2 in bats. Bats don't actually use language, but many species use vocalizations for navigation and locating prey. Previous work has shown that the echolocation skills of bats are rather complex. There are at least two styles of echolocation in bat species, bats can tune their vocalizations to specific needs, and they undergo vocal learning, modifying the sounds they generate in response to what they hear other bats doing.

The authors recognized that many of the parts of the brain involved in bat echolocation are already known to express FOXP2, so they sequenced the gene in a large number of bat species. In contrast to the rare changes seen elsewhere within the mammals, bats have many diverse forms of this gene—they are far and away the biggest outliers when the degree of sequence differences among mammals is plotted. These changes appear to be significant, as they clustered into two branches that correspond to the two styles of echolocation. Most of the changes were found in two specific locations within the gene, suggesting that new or altered activities were being selected for, while at the same time the basic structure of the gene was being conserved. Incidentally, no bats have both of the changes seen in the human version of FOXP2, although a number carry one of them.

The data isn't robust enough to confirm that FOXP2 is under positive selection, but the results are certainly suggestive. There are also a few results that, although they might be considered unexpected, actually support the view that FOXP2 helps enable vocal echolocation in some way. Some of the data was not significant unless fruitbats were omitted, but those species obviously don't hunt their stationary prey via echolocation. The authors also showed that toothed whales, which also hunt by echolocation, do not have a diverse FOXP2 gene. But these cetaceans don't rely on the normal mammalian vocalization mechanisms, using instead a specialized organ in the head to create sounds.

Where does that leave us in terms of understanding FOXP2 activity? The results clearly strengthen a direct connection between the gene's function and vocal activity. But, beyond that, they don't bring us any closer to knowing how: any combination of sensory, learning, and muscle control functions remains consistent with these results.